ERCC4 and xeroderma pigmentosum group B: We hypothesized that genetic polymorphism in other NER genes, such as XPB (Xeroderma pigmentosum group B), XPC (Xeroderma pigmentosum group C) and XPF (Xeroderma pigmentosum group F), which have not been studied, may be related to an individual’s susceptibility to benzene toxicity.